Generally, in the prior art, the catalyst is prepared in two steps:
(a) the carrier is prepared or bought on the market, PA0 (b) an activating phase is then deposited on the carrier. It contains generally (.alpha.) at least one metal mostly from group VIII of the periodic classification of elements, generally present in the catalyst as metal or for example as oxide or sulfide and (.beta.) optionally at least one socalled additional metal (or promoter) from any group of the periodic classification of elements, generally present in the catalyst as oxide or sulfide for example. PA0 (1) admixture of a charge, a binding agent and at least a portion of the active phase, PA0 (2) shaping of the mixture, PA0 (3) drying and optionally roasting, PA0 (4) optional introduction of the remaining portion of active phase, followed with a drying and then an activation. PA0 (1) during an optional first step, the material used as carrier is washed. PA0 (2) during a second step, the material used as carrier is dried by any adequate method, for example by stove-drying, so as to obtain a powder which keeps the same structure as the starting material and which, after drying, is characterized by a loss on heating of about 15-40% at 1000.degree. C. PA0 (3) during an optional third step, the material is washed and dried. PA0 (4) at this stage, before the subsequent steps, it is often preferable to roast at least partially the dried powder. Thus, 20-80% of the alumina powder can be subjected to a temperature of about 200.degree.-800.degree. C. and the roasted powder can be admixed with the non roasted powder. Here the advantage is to impart to the products to be obtained, a macro-porosity by means of two-phase products. More precisely, it is desired to obtain here, after admixture of the roasted powder with non-roasted powder, a powder of particle diameter ranging from 1 to 50 microns and having a critical macro-porosity corresponding to pores of a diameter larger than about 600 .ANG.. PA0 (5) then, the resultant powder is shaped:
According to the prior art, several methods may be used to incorporate the active phase of the catalyst into the carrier:
Generally, each metal individually or all the metals together may be incorporated to the carrier by means of a suitable method, consisting of a co-precipitation or cogelation with the porous carrier or an ionic exchange with the gelated carrier or further an impregnation of the carrier, either before or after the drying and roasting of the latter.